From owner-freebsd-hackers  Wed May 23 10:38: 9 2001
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Date: Wed, 23 May 2001 10:38:00 -0700 (PDT)
From: SJ <sandejain@rocketmail.com>
Subject: Re: Device driver questions
To: Alexander Langer <alex@big.endian.de>
Cc: freebsd-questions@FreeBSD.ORG, freebsd-hackers@FreeBSD.ORG
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--- Alexander Langer <alex@big.endian.de> wrote:
> Thus spake SJ (sandejain@rocketmail.com):
> 
> Hi!
> 
> > 1. "ioconf.c" contains struct config_resource and
> >     config_device definitions for declarations in 
> >     "config" file. But I noticed that for some
> devices
> >      e.g. device          atadisk
> >           device          atapicd
> >           ...
> >      the corresponding lines in ioconf.c are
> missing??
> 
> I think it's because ata is a self-identifying bus.
> Not sure, though.  Are any PCI-only devices listed?

The configuration contains the following two lines:
device          pci0
device          pci1
for which the corresponding ioconf.c output is:
struct config_resource pci0_resources[] = {
};
#define pci0_count 0
struct config_resource pci1_resources[] = {
};
#define pci1_count 0

> 
> > 3. File naming question:
> >    whats the reasoning behind having "bus.h" and 
> >    "bus_private.h"....whats the significance of 
> >    "private" here.
> 
> drivers include bus.h, kernel does also include
> bus_private.h

But still the name "private" confuses me...according
to
me it should have been "bus_public.c". Any comments?

thanks for your help
sandeep

> 
> > 4. concept behind having devclasses...I know that 
>  
> >    devclasses for a particular bus holds devices
> and
> >    device drivers for that bus. But then whats the
>  
> >    need for defining a devclass for each driver we
> 
> >    write ?
> 
> Because you can hold multpiple devices that are
> enumerated, e.g. xl0,
> xl1, ...
> The devclass is unique for each driver, but not for
> different busses.
> You can have ed0 on ISA and ed1 on PCI for example,
> using the same
> devclass.
> If ISA and PCI subdrivers are using a different
> devclass, the
> enumeration breaks.
> 
> > 5. Any poniters to literature which explains the 
> >    design philosophy and code specific help for
> device
> >    drivers in freebsd - I am referring to files 
> >    kern/subr_bus.c, bus.h, bus_private.h, isa/*
> etc.
> 
> Use the source, luke :-)
> Seriously, subr_bus.c is quite nice to read if you
> read it togethers
> with, say, sys/pci/pci.c.
> That makes the concept quite clear.
> 
> The developer's handbook might be worth reading for
> you, also there
> are some tutorials on the website which explain a
> little.
> 
> Alex
> 
> -- 
> cat: /home/alex/.sig: No such file or directory


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